Do we 'evolve' during our lifetime ? or do we only evolve as a species by passing on physiological 'lessons learnt' through reproduction ?

a) what is the best age to have children (evolution wise) ? Is there a best age ? Is it the same for both men and women ? Would the children I have now be better 'evolved' than those I could have had in my twenties ?

b) does the evolutionary effect come equally from both sexes ? If men create sperm throughout their lives, but women are born with all their eggs (correct me if I'm wrong) then can both sperm and eggs receive evolutionary changes prior to reproduction ?

c) is there a cut-off age by when men shouldn't have children i.e. for the health of the child ?

NB. yes I accept that a lot of behavioural & intellectual evolution comes though living a life - but that's not the question here.

Thank you for your replies - having never studied Biology, my question(s) was prone to include my own 'misconceptions' [thanks Matthieu M you gave me answers and you made me laugh too !]. To continue the conversation, I'd like to ask the questions below. Take your pick which you'd like to answer.

1) Could someone clearly (!) define the main differences between Lamarckian & Darwinian theories of evolution ... for a non-scientific audience ? Thanks.

2) The conversation below seems to focus on physical evolution. What other types of evolution do we experience through Epigenetics ... i.e. intellectual, emotional ?

Aug 27 2011:
Before Darwin erupted on the scene with his theory of evolution, the naturalist Jean-Baptiste Lamarck hypothesized that parents passed on experiences they had acquired during their lifetime. This was used to explain the giraffe's long neck for example, the idea being that a giraffe would pull its neck to the maximum and that this new configuration would be inherited. No attempt was made to understand exactly how these characteristics could be passed down. Occasionally, for the sake of sensation, people will try to revive Lamarckism.

Darwinian evolution is the specific inheritance of genetic material. Whatever you do in your life may have no impact on what you pass on as long as you fill in two crucial conditions: Survive and reproduce. Evolution work through random mutations and natural selection. Those mutations, which occasionally occur, can confer a selective advantage or conversely be a handicap (which in turn affects reproductive success). Obviously these changes aren't straightforward which is why they take many generations (so don't worry about the effect of evolution on your offspring). At any rate, the traits that are expressed through genes, don't get changed. They may be expressed differently depending on your environment, but they remain the same genes and are passed as is to the next generation.

So if we look at the giraffe example, imagine a tall tree and giraffes that are just about tall enough to get the closest fruits. A genetic mutation leads to a slightly longer neck for one giraffe which means that this giraffe has access to more fruit higher up. That way it doesn't need to compete with other giraffes for food and that gives it a survival advantage. As it reproduces, more and more of this kind survive over the older kind and soon there are many giraffes with longer necks. On the other hand, a giraffe with a mutation which stunts the growth of its neck, dies for starvation, the deleterious mutation is not passed on.

Aug 27 2011:
Epigenetics concerns itself only with the inheritance of physical properties that are non-genetic. It's still a fuzzy term because it's a fairly recent concept. (Only a few decades) Some crude intellectual and emotional properties will be inherited through genes. However, these are mostly things that develop during your life that are unique to you. Your interests, your personality and your intelligence is only loosely based on what you've inherited and tremendously influenced by your education, your upbringing and other things not related to evolution.

Aug 22 2011:
The thing to take note about is that humans have been evolving in a different way than standard evolution states for quite some time. Sure, that natural process is still proceeding with its slow pace, but humans manipulate our environment to suit our needs. If something isn't habitable or comfortable or efficient we will find a way of changing our surroundings so they are more so.

Effects on DNA are what most contribute to what I assume is your fear of having less than ideal offspring, but there are so many other factors involved, most of which are not properly understood at this point. What effect does cell phone usage have on sperm count? Negative apparently discovered recently. More importantly however, what effect does that have on sperm quality? On the likelihood of defects or mutations? What about all the other forces we haven't thought to take into effect? What about altitude, geophysical locations, emotional intensity throughout the lifetime, stress, natural chemical emissions in the body. All these things when properly understood will be able to make the answer to your questions much easier, but for now I'm afraid instinct and rational thinking seems to be the key. I wouldn't wait until you are late 60's but being as we don't understand everything, when you are in your late 60's DNA repair of sperm/egg cells might be possible.

Aug 22 2011:
1st title question: No. Evolution takes place with the spread of genes in populations. The dynamics of genes only change with the increase of decrease of beings carrying those genes (through offspring or the lack of). Evolutionary change takes place on larger time-scales.

2nd title question: What you are describing here is Lamarckism, an explanation for change in organisms that has not stood up to scientific scrutiny and was supplanted by Darwin's evolution by natural selection. There are no physiological lessons learnt per se in evolution, but non-random selection of randomly varying replicates. There are some interesting developments from the field of epigenetics (that is, the physical inheritance of traits other than genetic) that suggest that some aspect of genetic organization (DNA methylation) constitute acquired characteristics which will have been impacted by environmental factors within a lifetime. It is debatable whether this is a form of weak Lamarckism.

The best age to have children does not strictly depend on evolution, but more on the ageing process (which is a product of evolution) which correlates with increased damage in the body (so an increased risk of genetic defects for gametes).

Expressions like 'better evolved' don't mean anything. Better adapted to a current environment might be more appropriate. At any rate, unless a child is genetically impaired, having it at different times should have no incidence on adaptiveness.

I'm not sure what you mean by evolutionary effect, but here are some interesting facts: In terms of genetic contribution, women contribute more DNA to their offspring than men. This is because while they offer the same amount of nuclear DNA, only women pass on mitochondrial DNA. Women also pass on a lot of epigenetic characteristics from conception to birth. Another fact is that sperm has a higher mutation rate partly for the reason you suggested but not exclusively.

a) The safest age to have children is below the age of 35 give or take a few years. This is a loose reference range; as you know everyone is different biologically. The main reason is that genetic mutations accumulate throughout our life but accumulate faster in older age. This of course also depends on lifestyle choices that affect health. The females fertility will deteriorate faster because of the limited number of eggs produced (menopause can start from late forties).

Males will produce sperm throughout their lives but the quality (motility, concentration and morphology) or the sperm cells will also deteriorate later in life, though at a slower rate. It will not be 'better evolved' later in life as it is far to small an amount of time (say one child at 25, another at 35) for any beneficial mutation to have an advantage over the previous child.

b) Evolution (though recent research is giving new insights all the time) through natural selection uses the recombined genetic material of parents being passed on to create the child. The eggs/sperm (gametes) will not evolve in the ovaries/testes though when they combine to create the zygote (pre-embryo) they will create a different mix every time, which is why the resulting child cannot be predicted (at the moment any way, Sci-Fi films show an interesting future!).

c) As far as I'm aware, men may be fertile all their lives. Sperm quality deteriorates as early as 30's. But as for a cut-off for safety sake, If a sperm cell is of low quality, say low motility or morphological abnormalities (bent tail, abnormal shaped head etc), then it simply won't be able to penetrate the egg. The spermatozoa needs to be a fast healthy cell in order to make the arduous journey through the female genital tract. So its not necessarily dangerous (though it may be for older females (child and mother)), just less likely, though it isn't recommended to leave it too long.

Aug 19 2011:
Genetics has become more complicated with the new understanding about the way the genome is read out. This research is called epigenetica what shows that the way the genome expresses itself can change over lifetime and is passed on to the next generation if sperm or eggs are not yet formed. With males that is before puberty and with females in the womb of the mother. RNA has a role in reading DNA and as it is passed down on the female line you could conclude that the imprint of the female is more significant.
The best age to have children depends on the way you've lived your life and under which circumstances.
I wouldn't think of it all as evolving because humans are physically more or less perfect beings for millions of years. It has more to do with adaptation under various circumstances.
There is a lot more to it all and I know just a bit of it but maybe this is something of an answer.

We are still learning, and there are still many things unexplained, and I adree that Darwinism is a great lauching point. Yes there are some basic laws that we have come to agree apon, but still new things are discovered all the time that don't always fit and have flaws when it comes to some of those basic theories. Science is always evolving with each new discovery.

But where do instincts come from, or feelings of deja vu of a place you've never been but come to find out that a parent or ancester had been there before your birth?

Keep your mind open and don't burn all those people at the cross for thinking that not everything in the heavens revolve around the Earth

Aug 25 2011:
Curtis, I am all for keeping an open mind, but you simply cannot answer with the affirmative just because you speculate that some discovery in the future might make you right (not to mention that you made no attempt to justify your position). That's intellectually dishonest and misleading for someone who confuses a few concepts as Chris does. I have already mentioned epigenetics in my earlier post if you would like to refer yourself to it. It certainly does not overlap with the concepts of physiological lessons learnt or evolution in an organism's lifetime. Epigenetics is like quantum mechanics in the sense that it already has a strong scientific establishment behind it, but the laymen are confused about it and use it as an excuse for all sorts of concepts they wish were true.

When answering a scientific question apply to your answer the scientific rigour you would expect from scientists. At the very least, have the decency to start with "I think".

Aug 24 2011:
There's a serious lack of scientific rigour in a lot of these postings. I'd appreciate if those who don't know enough about evolution please refrain giving their opinion like they're certain it's true. In that respect I like Daniel's answer because even though he seems to get it right, he is humble enough to finish his post by "I think". A lot of people here seem to not be able to tell Lamarkism and Darwinian evolution apart. There's a crucial difference.

To Title question: yes, we contribute to 'evolution' of human being for sure, even in our lifetime. What we all witness is, here in China more and more people abandon rural labor work, they get proper education, do not need strong arms and legs; which means more people get slimmer and slimmer, naturally their children won't be strong as well.

Normally visible changes in evolution might take centuries or even longer, but in this information era, there is a trend that human beings are getting less strong, but smarter in quite short time ( say, a few decades ).

To a): there is some guidance from government or institute about best age to have children, but that's from health point of view, rather than 'evolution wise'.

To b): yes, of course.
To c): There should be, but it varies from case to cases. In China, Confucius's father was over 70 years old to have him, and he's smart enough to become a great teacher and have huge impact to Chinese culture.

Aug 24 2011:
a) Whenever the parents believe they're emotionally, physically, and most importantly financially ready. I want to have my kids early in life so I'm not in my 50s when they're teenagers.
b) Sperm has more time to evolve however by that time men aren't having kids. Also any major strides in evolution in the process of making a human would take centuries to occur.
c) They shouldn't have children in their 50s but mid 40s would be acceptable however they won't be alive or active enough so I'm sure they'd regret the decision.

Aug 25 2011:
How does the baby bird know that eating the Monarch Butterfly will make it ill without ever eating it, or that it takes several generations of Monarch Butterflies to complete the migration cycle from Mexico to Canada and back?

Those two examples come quick to mind.

Many things get passed down in many ways. But as we make the world safer, stupidity gets passed down more and more instead of being eaten by wild animals...

Aug 25 2011:
Baby birds that eat monarch butterflies die from poisoning, baby birds that avoid monarch butterflies don't. Eventually genes for monarch aversion start to dominate. As for the migration, again behaviour acquired through monarchs that make the trip when the time is right surviving over those who don't.

It's not up for debate, Lamarckian evolution simply does not take place, only Darwinian evolution. Knowledge and stupidity are passed down through culture not genes, that's not evolution. Chris was quite specific about what he means by evolution (even though some of this question are based on misconception, which is ok when you're asking a question, but not really when you're answering it).

Aug 22 2011:
Actually i didn't quite catch your question, but anyways leaving apart intellectual & behavioral evolution ! suppose imagine your stuck in a different environment than the present, hmm like your doomed to spend your rest of your life in a place the temperature is always below -5 and the place has serious lack of technology. you start adapting yourself (or you die) to that environment body brings some physical changes isn't that evolution ?

Aug 19 2011:
Recwent discoveries indicate that sexual reproduiction is more a function of immunity than diversity. Taking a look at the "Cambrian Explosion" with a "sudden" appearance of different forms adapted to their own environment niche, it is possible to conclude that this "explosion" was the result of viral DNA in a constant and massive swapping, "cut and paste", with a gradual collection in which DNA in each organism began to function cooperatively to exclude damaging DNA. IOW, immunity developed fiorst in the replication of organisms, with each one specifically adapted to certain envirtonmental limitations.

Sexual reproduction, it would seem, developed by the reduction of certain DNA "grouped" within the male and female of a species, with the sperm acting to "inform" the egg of necessary information within the environment. Sexual reproduction, therefore, is an extension of immunity within an environment, not diversity.

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